A conventional variable valve mechanism disclosed, for instance, by Japanese Patent Laid-Open No. 63023/1995 changes the lift amount of a valve body in an internal combustion engine that is equipped with the valve body, which opens/closes in synchronism with camshaft rotation. This variable valve mechanism is provided with a swinging arm that is positioned between a cam and valve body to swing in synchronism with a cam operation. The swinging arm is built in the internal combustion engine in such a manner that its basic relative angle in relation to the valve body is variable. Further, the mechanism includes a lost motion spring and adjustment mechanism. The lost motion spring controls the motion of the swinging arm by directing the swinging arm toward the cam. The adjustment mechanism changes the relative angle of the swinging arm to the valve body in accordance with control shaft rotation.
In the variable valve mechanism described above, the lost motion spring works so that the cam is in constant mechanical contact with the swinging arm. Therefore, the variable valve mechanism can constantly transmit the mechanical force generated by the cam to the valve body without any loss. Further, the variable valve mechanism can change the reference relative angle of the swinging arm to the valve body by rotating the control shaft. When the relative angle changes, the time (crank angle) required for the swinging arm to start depressing the valve body can be changed after the cam's pushing pressure begins to be transmitted to the swinging arm, that is, after the swinging arm begins swinging due to cam action.
When the time required for the swinging arm to start depressing the valve body changes, the crank angle width (hereinafter referred to as the “operating angle”) for placing the valve body in a non-closed state changes so that the profile of the lift amount for the valve body changes. Therefore, the conventional mechanism described above can change the operating angle and lift amount or the valve body with a high degree of freedom.
Including the above-mentioned document, the applicant is aware of the following documents as a related art of the present invention.
[Patent Document 1] Japanese Patent Laid-Open No. 63023/1995
[Patent Document 2] Japanese Patent Laid-Open No. 293216/1995